1. Field of the Invention
The present invention relates to a laser survey instrument which emits a visible laser beam.
2. Description of the Related Art
In a survey instrument (laser planer) in which a scanning laser beam is rotated to project a plane beam in the vertical or horizontal direction, the beam can be easily viewed at a close distance, but it is difficult to view the beam at a long distance since the amount of light per unit length is reduced. One solution to enhance the visibility is to reciprocally rotate the head within a predetermined angle range without rotating the same over the angle of 360 degrees to thereby increase the amount of light per unit length. For example, Japanese patent No. 2,829,912 discloses a visible laser survey instrument in which a scanning motor is rotated in the forward and reverse directions so that the reciprocating-scan angle set by a reciprocating-scan angle setting circuit is identical to the reciprocating-scan angle detected by a reciprocating-scan angle detection circuit.
In this known laser survey instrument, if the reciprocating-scan angle is too small, it is impossible to obtain a sufficient length of linear beam at a close distance. Conversely, if the reciprocating-scan angle is too large, the amount of light at a long distance is reduced, so that it is difficult for an operator to view the beam. Therefore, in order to obtain an optimum amount and length of beam, it is necessary for an operator to manually vary the reciprocating-scan angle in accordance with the distance.
It is an object of the present invention to provide a laser survey instrument in which an optimum reciprocating-scan angle of the laser beam is automatically obtained in accordance with the distance of the laser beam at which a plane is drawn by the laser planer.
In general, a conventional laser survey instrument is provided with a adjusting device which adjusts the beam waist position of the laser beam (at which the minimum beam diameter is obtained) to make the beam waist position coincident with an object (target). In the basic concept of the present invention, the reciprocating-scan angle is varied in accordance with the beam waist position, so that the visibility of the beam can be enhanced, regardless of the reciprocal scan length.
According to another aspect of the present invention, a laser survey instrument is provided, including a laser source; a beam waist position varying optical system having a movable lens group through which a laser beam emitted from the laser source passes, so that the movement of the movable lens group in an optical axis direction causes the beam waist position of the laser beam to vary; a rotatable head portion from which the laser beam transmitted through the beam waist position varying optical system is emitted; a reciprocating-scan angle setting device for setting a reciprocating-scan angle of the rotatable head portion in accordance with position data of the movable lens group of the beam waist position varying optical system; and a head portion controller for reciprocally moving the head portion by the reciprocating-scan angle.
In an embodiment, the reciprocating-scan angle setting device utilizes a table stored in a memory in which a relationship between the position of the movable lens group of the beam waist position varying optical system and the reciprocating-scan angle of the head portion controller is stored, so that a corresponding reciprocating-scan angle can be selected based on the position data of the movable lens group.
In an embodiment, the reciprocating-scan angle setting device calculates a reciprocating-scan angle of the head portion based on the position data of the movable lens group of the beam waist position varying optical system in accordance with a predetermined relationship between the position of the movable lens group and the reciprocating-scan angle of the head portion, the predetermined relationship being stored in a memory.
Preferably, the beam waist position varying optical system includes a motor, and a feed screw mechanism which is driven by the motor to move the movable lens group.
The position data of the movable lens group of the beam waist position varying optical system can be detected in accordance with either the rotational angular displacement of the motor, or the rotational angular displacement of a rotating member rotated by the motor.
In an embodiment, the beam waist position varying optical system is accommodated in a hollow shaft member, and the rotatable head portion is provided at the top of the hollow shaft member.
In an embodiment, the beam waist position varying optical system includes a positive lens group which is immovable, and a negative lens group which is movable.
Alternatively, in another embodiment, the beam waist position varying optical system includes a positive lens group which is movable and a negative lens group which is immovable.
According to another aspect of the present invention, a laser survey instrument is provided, including a hollow shaft member having an axis; a rotatable head portion provided at the top of the hollow shaft member to be rotatable about the axis of the hollow shaft member; a beam expander accommodated in the hollow shaft member, the beam expander comprising at least a positive lens group and a negative lens group, wherein one of the positive and negative lens groups comprises a movable lens group which is movable in the optical axis direction; a laser source to emit a laser beam through the beam expander and rotatable head portion, wherein the laser beam exits from the rotatable head portion in a direction perpendicular to the axis of the hollow shaft member; a position detector which detects the position of the movable lens group of the beam expander; a reciprocating-scan angle setting device for setting the reciprocating-scan angle of the rotatable head portion in accordance with position data of the movable lens group detected by the position detector; and a head portion controller for reciprocally moving the head portion by a set reciprocating-scan angle set by the reciprocating-scan angle setting device.
In an embodiment, the reciprocating-scan angle setting device utilizes a table stored in a memory in which a relationship between the position of the movable lens group of the beam expander and the reciprocating-scan angle of the head portion controller is stored, so that a corresponding reciprocating-scan angle can be selected based on the position data of the movable lens group.
Preferably, the movable lens group of the beam expander is driven by a motor and a feed screw mechanism.
In an embodiment, the position detector of the movable lens comprises an annular position detector which detects the rotational angular displacement of the motor or the rotational angular displacement of a rotating member rotated by the motor.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 11-247306 (filed on Sep. 1, 1999) which is expressly incorporated herein by reference in its entirety.